A wide variety of industrial, pharmaceutical, animal and food products rely upon foamed or aerated structures. The capacity of such foams to ingest and retain gasses largely depends upon the functional attributes of its hydrophilic film-forming component. Certain naturally occurring hydrophilic film-formers, such as casein and egg albumin, are inherently excellent foam producers and do not require additional or supplemental foaming components. The essential foaming components are apparently indigenously present in such proteinaceous foaming compositions. In contrast, most other hydrophilic film-formers, especially the synthetic foaming compositions, typically require supplemental foaming additives (e.g. foam stabilizers, emulsifiers, thickeners, etc.) to achieve satisfactory foaming properties. The presence of these supplemental additives normally create more serious foaming problems than they correct. These foaming problems limit such synthetic foaming compositions to specific applications. The versatility and overall foaming efficacy of the naturally occurring protein foaming agents (e.g. egg albumen or casein) are generally recognized as superior to those foaming compositions formulated with the synthesized film-formers, including those extensively modified (chemical, physical, enzymatic, etc.) animal or plant proteins.
U.S. Pat. No. 3,814,816 by Robert C. Gunther discloses a pepsin-modified soy protein hydrolyzate foaming agent. These soy protein hydrolyzates are typically made by initially chemically hydrolyzing soy protein followed by digestion with pepsin. Commercially available pepsin modified soy protein whipping agents under this patent typically are water-soluble throughout the pH 4.0-7.0 range (20% dry protein solids concentration) and remain stable against heat denaturation at temperatures between 25.degree. C.-180.degree. C. Comparative to the numerous other synthetic whipping agents, these pepsin-modified soy hydrolyzates possess exceptional whipping properties. In U.S. Pat. No. 4,120,987 by Moore, conventional phosphate stabilizers (e.g. ammonium, alkali or alkaline earth metal salts of phosphate and polyphosphates) are disclosed as possible confectionery recipe additives.
Within recent years, the paper industry has utilized foams to coat or size paper products. A recently issued patent by Jenkins (U.S. Pat. No. 4,184,914) discloses "hydrolyzed protein foaming agents capable of reducing surface tension of water from a normal value of 72 dynes per centimeter to a minimum value in the range of from 45 to 65 dynes per centimeter as a functional additive for paper coating applications. Illustrative hydrolyzates disclosed by the Jenkins patentee include "keratin or albumin such as hoof and horn meal, feathers and blood." Conventional whiteners, or water-insoluble pigments, such as calcium carbonate reportedly may also be formulated into such foaming compositions. Conventional fire fighting foaming compositions which contain the hydrolyzed proteins are also reportedly applicable to this paper coating technology.
British Patent Specification No. 1,368,463 discloses that magnesium chloride, calcium chloride and ethylene glycol are conventionally added to fire fighting foams as anti-freeze additives. Such anti-freeze additives are disclosed as causing precipitation of the surfactants. The surfactants are reportedly essential for foaming. Formamide is proposed as an anti-freezing agent replacement since it will not affect the surfactant functionality in the foaming system. The benefits of using Pyrene Plus F (a fire foam composition) formulated with formamide as an anti-freezing agent instead of magnesium choloride are reported in Example 1. Chemical Abstracts, Vol. 84 also reports that foaming agents, water-, heat- and chemical-resistant and stable foams for cement products and fire extinguishing applications may be obtained by combining the alkali hydrolyzate products of microbes with certain metallic salts.
The ability of certain proteins to form metal complexes (chelation) is known. A general review of this chemistry is disclosed in The Handbook of Food Additives (2nd Ed) by Furia (CRC Press (1972)). According to Furia; "For chelation to occur two chemical conditions must be satisfied: (1) the ligand must have the proper steric and electronic configuration in relation to the metal being complexed and (2) the surrounding milieu (pH, ionic strength solubility, etc.) must likewise be conducive to complex formation." Illustrative metal/chelating agent complexes disclosed by Furia include: barium, calcium, cobalt, copper, ferrous, ferric, magnesium, maganese, nickel, strontium and zinc ions.
Foams are complex. Certain additives conducive to satisfactory foams in certain systems will often adversely affect other systems. Within the field of proteinaceous materials, it is possible to derive an unlimited number of different film-forming compositions by physically, chemically or enzymatically altering or modifying the protein molecule. Such divergencies apparently arise because of the infinite compositional, molecular, steric and electronic configuration differences therebetween. As a general rule, most proteinaceous film-forming materials (modified or unmodified) are ineffective foaming agents. Even amongst the recognized protein foaming agents, such as egg albumen, casein; different foaming attributes and compatibility with other recipe additives exist. Certain foaming applications will require the unique foaming functionality and compatibility of egg albumen while others will require casein. Additives complementary to egg albumen foam often destroy the unique foaming efficacy of casein.
The desirability of a low-cost, whipping protein has long seen sought by the art. The vegetable proteins are recognized as a low cost protein source, but generally possess inadequate whipping properties to compete with egg albumen and casein systems. In the art's attempt to improve upon the whipping efficacy of vegetable proteins, a host of chemical, enzymatic and physical processing modifications have been suggested.
The inventors sought to improve upon the foaming efficacy of proteinaceous materials and particularly those which are obtained from abundant and low cost raw materials. It has been discovered that a combination of certain metal ions and protein hydrolyzates will unexpectedly yield superior foams. Laboratory evidence indicates certain water-soluble proteinaceous materials apparently possess at least two different chelating sites which require at least two different types of chelating metal ions to obtain an improved foaming effect. Within the field of soy protein, only certain types of hydrolyzates appear to possess this multi-site functionality. As a result of their discovery, it is now possible to achieve the unique foaming attributes of egg albumen and/or casein from a vegetable protein source. The foaming compositions of this invention may be used in a wide variety of industrial, pharmaceutical and food applications.